Three-dimensional seismic surveys are typically designed to have an approximately uniform spatial distribution of sources and receivers over the survey area. Because conditions in the field are less than ideal, the design geometry cannot be perfectly implemented and the actual distribution of sources and receivers is more irregular than desired. Irregular geometry (too many sources and receivers in some locations and too few in others) violates the assumptions made by commonly used imaging algorithms, resulting in a distorted image of the subsurface. The most commonly recognized type of distortion is the “acquisition footprint”—spurious amplitude variations that are associated with the interaction between acquisition geometry and the imaging algorithm. These amplitude artifacts may interfere with interpretation of truly geologic variations in the amplitude of the reflector.
Because amplitude artifacts associated with irregular geometry may negatively impact an interpretation, it is common practice to acquire additional seismic data to fill in areas of reduced coverage. For a typical marine streamer survey, infill acquisition increases the amount of data by about 20%, with an accompanying increase in cost. The increase can be significantly larger for surveys that encounter operational problems.
Decisions about acquiring infill are currently made qualitatively, based on visual inspection of a coverage map. Coverage maps are produced by a commercially available binning system on the seismic vessel, such as the REFLEX binning system produced by Concept Systems Ltd. Coverage maps account only for the surface positions of the source-receiver pairs recorded in the survey; they do not account for the effect of imaging. From the coverage map, quality control personnel make a qualitative judgement about the potential effects of irregular coverage on an interpretation and about the economic tradeoff between increased acquisition cost and possible impact on future drilling results. Because infill decisions are almost purely qualitative, it is difficult to insure that the optimum amount of infill has been acquired.
Methods that account for the effect of imaging have been described in the literature by Calderon et al., “Efficient computation of 3D acquisition footprint analysis, 69th Ann. Internat. Mtg., Soc. Expl. Geophys., 1489–1492 (1999); Schneider and Winbow, “Efficient and Accurate Modeling of 3-D Seismic Illumination,” Expanded Abstracts, 69th Ann. International Mtg., Soc. Of Expl. Geophys., pp. 633–636 (1999); Laurain et al., “Towards better amplitude maps by simulator migration,” Expanded Abstracts, 72nd Ann. Internat. Mtg., Soc. Expl. Geophys. (2002); U.S. Pat. No. 6,131,070 to Ferber (2000); and U.S. Pat. No. 6,343,256 to Winbow et al. (2002). Compared to coverage maps, these methods provide more realistic estimates of the level of amplitude artifacts that will result from any specific irregular arrangement of sources and receivers. However, no existing approach attempts to quantify the effect that the artifacts will have on an interpretation of the seismic data, and no existing approach quantifies the loss in economic value that is caused by the artifacts. The present invention satisfies these needs.